This invention generally relates to ink jet printer apparatus and methods and more particularly relates to apparatus and methods for cleaning a print head.
An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. So called xe2x80x9ccontinuousxe2x80x9d ink jet printers utilize electrostatic charging tunnels that are placed close to the point where ink droplets are being ejected in the form of a stream. Selected ones of the droplets are intercepted downstream, while other droplets are free to strike a recording medium. In the case of xe2x80x9cdrop on demandxe2x80x9d ink jet printers, ink droplets are ejected from selected nozzle orifices only when needed.
Of course, the ink jet print head, whether of the xe2x80x9ccontinuousxe2x80x9d or xe2x80x9cdrop on demandxe2x80x9d type, is exposed to the environment at the nozzle orifice opening, which are exposed to many kinds of air born particulates. Particulate debris may accumulate on surfaces formed around the orifices and may accumulate in the orifices and ink ejection chambers themselves. The ink may combine with such particulate debris to form an interference burr that blocks the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. The particulate debris should be cleaned from the surface and orifice to restore proper droplet formation. In the prior art, this cleaning is commonly accomplished by brushing, wiping, spraying, vacuum suction, and/or spitting of ink through the orifice.
An ink jet print head cleaner is disclosed in U.S. Pat. No. 4,970,535 titled xe2x80x9cInk Jet Print Head Face Cleanerxe2x80x9d issued Nov. 13, 1990, in the name of James C. Oswald, wherein heated air is directed past ink jet apertures on the head face and then out an outlet. However, use of heated air is believed to be less effective for cleaning than use of a liquid solvent. Also, use of heated air may damage fragile electronic circuitry that may be present on the print head face.
U.S. Pat. No. 4,600,928 by Braun et al., issued Jul. 15, 1986, teaches an ultrasonic self-cleaning system for cleaning of a print head assembly wherein ink is supported in approximation to the orifices of the print head by capillary force. Ultrasonic cleaning pulses are then applied to clean the surface through fluid transmission of that ultrasound energy to said surface.
U.S. Pat. No. 5,574,485 by Anderson et al., issued Nov. 12, 1996, discloses the use of ultrasonic energy in conjunction with a cleaning fluid to dislodge dried ink particles from a print head surface. However, this system requires a relatively complex cleaning station including apparatus for scanning the liquid wiper across the print head surface.
Therefore, there is a need to provide a self-cleaning printer and method of assembling same, which self-cleaning printer provides effective cleaning without complex cleaning station apparatus.
According to a feature of the present invention, a self-cleaning printer includes a print head having a surface that is susceptible to a contaminate build up. A cleaning liquid containing a concentration of macroscopic cleaning particles is flowed in frictive contact with the contaminate, during which forces are exerted on the contaminant by contact between the contaminant and at least one cleaning particle and energy is exchanged by contact between the contaminant and the cleaning particle, such that a combined effect of frictive force and the hydrodynamic shearing force of the liquid acting on the contaminate effectively removes the contaminate from the surface.
Preferably, the cleaning particles are adapted to attach to the contaminate. They may include polymeric beads such as polystyrene spheres. The cleaning particles preferably have surfaces to which polymeric chains are attached, the polymeric chains having end groups which adhere to the contaminate.